Ski boots are known comprising an outer shell of plastic material, a sole, a leg portion pivoted to the shell on bosses provided at the malleoli, a padded inshoe, and a plurality of closure hooks, laces, latches, etc. to immobilize the skier's let within the shell.
The shell generally presents a flexible portion (bellows0 in the region straddling the metatarsus of the foot, enabling the skier to bend the leg during walking.
To illustrate, U.S. Pat. No. 6,247,252, granted Jun. 19, 2001 to David Parisotto, discloses a telemark ski boot which possesses the desired characteristics of torsional rigidity, without penalizing flexibility in the area of the metatarsus. Such flexibility allows the skier to raise his, or her, heel, when facing a curve in his path, as contrasted with the rigid fastening of the heel to the ski, in the conventional skiing technique.
The flexibility in the ski boot of Parisotto '542 is achieved by flexible portion 11 , which extends transversely across the shell of the boot, as shown in FIGS. 1 and 3. The flexible portion presents an undulated profile defined by a pair of grooves 12 separated by an intermediate rib 12a. Stiffening elements 17, 18 join the inner sole of the shell, immediately behind the flexible portion, to maintain torsional rigidity of the ski boot, without interfering with the flexibility of the shell. The shell and the flexible portion of the ski boot may be formed from different plastics, with different levels of flexibility; a co-injection process is suggested.
U.S. Pat. No. 6,708,425, granted Mar. 23, 2004, to David Parisotto, discloses a ski boot, comprising a plastic shell, a shank or leg portion hinged to the shell for pivotal movement relative thereto, and a control mechanism, located at the rear of the boot, for controlling the tilt of the shank relative to the shell. A flexible portion 11, extending across the boot in the vicinity of the metatarsus, is formed by two grooves 12 separated by a radiused intermediate portion 12a. The ski boot is suitable for use as a ski-mountaineering boot, or a telemark skiing boot, as noted in column 1, lines 21-41, of Parisotto ′425.
However, these known ski boots represent certain drawbacks. In particular, possible accidental release of the front jaw and/or heel fixing unit from the binding, as the heel and toe of the boot tend to rise following boot flexure/deformation; weakening of the boot structure under torsional stresses, i .e. those stresses induced by guiding the ski; and difficulties in manufacturing and assembling the boots as the bellows are made separately from the shell, and must be inserted into the boot injection mold. This procedure also requires the shell to be closed at the rear of the region in which the bellows are applied. This requirement leads to difficulty in removing the boot from the mold and makes it necessary to use materials of low rigidity, which contribute to poor technical performance.